Skyrmion lattices in metallic and semiconducting B20 transition metal compounds.

High pressure studies in MnSi suggest the existence of a non-Fermi liquid state without quantum criticality. The observation of partial magnetic order in a small pocket of the pressure versus temperature phase diagram of MnSi has additionally inspired several proposals of complex spin textures in chiral magnets. We used neutron scattering to observe the formation of a two-dimensional lattice of skyrmion lines, a type of magnetic vortices, under applied magnetic fields in metallic and semiconducting B20 compounds. In strongly disordered systems the skyrmion lattice is hysteretic and extends over a large temperature range. Our study experimentally establishes magnetic materials lacking inversion symmetry as an arena for new forms of spin order composed of topologically stable spin textures.

Long-range exchange interactions and integer-spin S(t) = 2 EPR spectra of a Cr(III)Zn(II)Cr(III) species with multiplet mixing.

Synthesis, structural, and spectroscopic characterization of the linear cationic complex [LCr(III)(mu-[dmg)(3)Zn(II))Cr(III)L](2+) (1) in which L = 1,4,7-trimethyl-1,4,7-triazacyclononane and dmg is the dimethylglyoximato anion are reported. The Cr...Cr distance of 1 is 7 A. SQUID magnetic susceptibility measurements reveal the presence of long-range exchange interaction of the Cr(III) terminal ions, mediated by the diamagnetic Zn(II)(dmg)(3) "bridging ligand" (J(0) = -4.4 cm(-1), H(ex) = -2J(0)S(1)S(2), S(i) = 3/2). Multifrequency EPR measurements (S-, X-, Q-band) on frozen solutions were used to establish the intramolecular nature of the exchange coupling and to determine the zero-field splitting (ZFS) parameters and the anisotropic contributions of spin coupling. An effective spin Hamiltonian description was applied for interpretation of the spectra originating from the S(t) = 2 total spin manifold which included up to fourth-order terms for the ZFS. By the help of alternative simulations with the full coupling matrix for two spins S(i) = 3/2 (16 x 16) it could be shown that the higher-order terms in the effective description owe their origin to multiplet mixing due to competing single-ion ZFS (the absolute value of D(i) = 0.2 cm(-1)) and isotropic exchange interaction. The magnetic anisotropy related to dimer properties could be readily explained by dipolar coupling (j(z) = -0.012 cm(-1)). Implications for the interpretation of other integer-spin EPR spectra are discussed.